If your system came with Catalyst Control Center, there should be a setting there to adjust the overscan. This should increase the desktop display to match the size of your screen.
Well it does, but the problem is it wont let me use the slider. This is what I do, Start>Desktops and Displays>My Digital Flat-Panels> Scaling Options. I try to slide the slider from being all the way to the right which is overscan but I cant. Even when I click the box "Use the scaling values instead of the customized settings when the desktop resolution does not match your DFP resolution.
To add, the screen is low quality compared to my laptop screen also the windows are bigger and I don't know why.